Use a half-angle identity to find the exact value

Given:

To find:

The exact value of cos 15°.

Solution:

Using half-angle identity:

Using the trigonometric identity:

Let us first solve the fraction in the numerator.

Using fraction rule:

Apply radical rule:

Using :

first, we define the variables:

x: number of years after 1950

f (x): amount of vinyl sold.

then, with the variables defined, we have:

68594 vinyl records were sold in 1958 > f (8) = 68594

91299 vinyl records were sold in 1961 > f (11) = 91299

38720 vinyl records were sold in 1952 > f (2) = 38720

161743 vinyl records were sold in 1967 > f (17) = 161743

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step-by-step explanation: